[mordabdul1]

Summary

Closes #81.

Adds explicit named regression tests for the "0 disables" sentinel on both limits that share the convention, covering the sharpest inversion risk: resetting an active limit back to 0 (not just the never-configured default).

Tests added

• test_max_settlement_amount_zero_sentinel_disables_cap — sets a 500 cap and asserts a 600 settlement is rejected with AboveMaxSettlementAmount; then resets the cap to 0 and asserts a settlement for the entire pool (1,000, double the former cap) succeeds. 0 means "no cap", never "cap of zero, reject everything".
• test_min_liquidity_zero_sentinel_disables_floor — the cross-checked min_liquidity equivalent: an active 700 floor rejects a withdrawal with BelowMinLiquidity; resetting the floor to 0 lets the pool drain to exactly zero.

Both scenarios the issue names were already partially covered (test_max_settlement_amount_disabled_by_default for the untouched default, test_open_settlement_rejects_amount_above_cap / test_open_settlement_allows_amount_at_cap for nonzero-cap enforcement including the at-cap boundary); those remain unchanged, and the new tests add the explicit active→0 transition neither covered.

Review of the sentinel logic (no gap found)

• open_settlement guards with cap > 0 && amount > cap (src/lib.rs), so a zero cap short-circuits cleanly.
• require_min_liquidity early-returns Ok on floor == 0.

No fix needed in src/lib.rs.

Testing

Full suite: 155 passed, 0 failed. cargo fmt --check clean.

Incidental

Bumps ethnum 1.5.2 → 1.5.3 in Cargo.lock (1.5.2 fails to compile on recent rustc, E0512). Same patch bump as the other open PRs; merges cleanly in any order.